I've always ridden minimum 170 up to 175(standard)
Fitted some 165mm Middleburns to my SS and its like chalk and cheese.
I absolutely love them and shall be hunting out more sets to fit to my other steads.
I should add i am 5' 8" and 28.5" inside leg

I'm 6'2 also and tried 180s on my 'cross bike after years on 175s. It didn't work for me. Having to put the saddle down 5mm to keep the leg extension correct at the bottom of the down stroke meant the up stroke was 10mm higher. Felt really odd. Was nice to have the extra leverage in places and made it a little easier remounting but overall it felt slower.

I'm about to buy new cranks ready for the new build and considering trying 165mm to help make up for bad technic
6ft tall and use 175mm atm and regularly have pedal strikes.
What's the pros & cons of smaller crank arms?

Depends on what your trying to achieve.
And how long your legs are. I'm 6' with 34 inside leg (suits you sir) and use 172.5 on the mtb and 170 on the road. Longer cranks give more leverage for those big push moments but increase amount of movement required from knees and hips.
As I've got older I try to keep the pedalling going rather than pushing a larger gear. It definitely helps on longer road rides.
There are stories from the distance past of TdeF riders putting longer cranks on for the mountains. Cyrillic Guimard (hinault and Fignion manager) reckoned it put an end to his pro career.

Rode 180's on a singlespeed and they were horrible, too many pedal strikes and felt it was more effort in getting them spinning. The perceived extra torque I'd get with the longer arms on steep/tougher sections never really became apparent and ultimately the bad stuff outweighed the good.

I've 165's fitted to my Horsethief, made the change due to pedal strikes as I had 175's fitted, originally I was going to get a pair of 170's or so but read some bumf about shorter cranks and decided to try them. I've found that the pedal strikes almost vanished and I'm feeling I'm climbing better, they seem easier to spin and I don't think I need to get up out of the saddle as much. So for me a win, any cranks from here on in will be of the shorter variety.